Airspace around the Swiss village of Davos is restricted as part of the World Economic Forum every year. The amendment to the Austrian AIP instructs pilots who would still like to cross the affected airspace as follows:

How do I "address my flight plan" to a station other than the ATC at dept./arr. airports? The code given is also too long for an ICAO airport?

The code LOWWYWYW is an AFTN Address (Aeronautical Fixed Telecommunication Network), identifying an AFTN station. In this case a sub-structure of the ATC organisation of an international airport.
LOWW designates Vienna Int. Airport, while YWY designates a Military Flight Operational Control Centre. The final W is likely a filler. The final W designates yet another subdivision of YWY.
• The X in LOWWYNYX in the SUP header is an example of a filler that you mention, but the last W for the answer would be a subdivision of YWY per Doc 4444 11.2.1.2.3.2. Nice Q&A!